The present invention relates to a method of operating an elevator system, and an elevator system in which this method can be used.
Usually, elevator systems are used in which the elevator car is raised and lowered by means of a rope. Typically used as rope is a steel suspension rope that runs over a rope sheave and at one of its ends is connected to the elevator car and at its other end to a counterweight. The rope sheave is driven by an electric motor, the rope sheave raising the elevator car when the motor turns in one direction, and the rope sheave lowering the elevator car when the motor turns in the other direction. Between the drive motor and the rope sheave, a reduction gear can be provided. Typically, the drive motor is also provided with a control unit. The rope sheave, the drive motor, and a control system are usually arranged in a machine room above the elevator hoistway.
The elevator car and the counterweight hang on mutually opposite sides of the rope sheave. The weight of the counterweight usually corresponds approximately to the weight of an elevator car that is 40% full. If the elevator car is 40% full, the result is that only little energy is needed to move the elevator car. In such a case, the drive motor serves mainly to overcome friction. If the weight of the elevator car is approximately equal to the weight of the counterweight, this results in an approximately constant level of potential energy in the overall system. When the potential energy of the elevator car falls as a result of the elevator car being lowered, the potential energy of the counterweight increases correspondingly as a result of its being raised, and vice versa.
This normally used elevator system has the disadvantage that additional building space is required for the counterweight. Also, the moment of inertia of the counterweight can cause undesired positional changes of the elevator car.
These disadvantages can, however, be avoided by the rope, or a corresponding means of suspension, being wound around a drum that is provided for this purpose, instead of passing over a rope sheave and being connected on the other side to a counterweight. Such an elevator system is known from German patent application 2136540. Known from this application is an elevator system with a drive drum in which the suspension belt that is used as a suspension means is stored. The arrangement of a counterweight can thereby be obviated. The suspension belt is driven by positive engagement and does not depend on higher coefficients of friction between the suspension belt and the drive drum.
From U.S. Pat. No. 6,305,499 B1 an elevator system is known that also has a drum on which the suspension means is rolled so that a counterweight can be obviated. The drum is arranged in the elevator hoistway. The suspension means is fastened to a wall of the elevator hoistway, runs over two rope sheaves that are arranged on the elevator car, and is rolled onto the drum through an opening in another hoistway wall.
Since in the known elevator system with drum, the suspension means is rolled onto the drum at a constant rotational speed, the speed of the elevator car changes depending on the length of the suspension means already rolled onto the drum. As the elevator car rises, the suspension means is rolled onto the drum, as a result of which the diameter of the roll of suspension means on the drum continually increases, which in its turn results in an increase in the speed of the car. When the elevator car travels down, the diameter of the roll of suspension means decreases, with the consequence that the speed of the elevator car reduces. If the speed of rotation of the drive unit is constant, the speed of the elevator car thus depends on the position of the elevator car. This results in a low level of comfort for the user.